The invention relates to a brake system for a motor vehicle.
As is it known, hybrid vehicles have the problem that the rear axle, when driven electrically, should recuperate to a maximum during a braking engagement, and that the mechanical brake system—which is connected to the electric motor in parallel—decelerates as little as possible at the same time. The reason is that a greatest possible proportion of the braking energy should be converted into electrical energy. Due to different circumstances, the recuperation power of the electric motor battery assembly is, however, not constant but dependent on various constraints, like e.g. the charge state of the battery, the operating temperature of the electric motor, etc. Therefore, it is desirable that the brake system is blending-capable, i.e. that a flexible split of the brake power between recuperation and hydraulic brake system is rendered possible.
A method and device for recuperation of energy during a braking process of a hybrid vehicle is disclosed in DE 10 2005 039 314 A1. The disclosed blended brake system includes a pressure reduction valve, by which the brake pressure applied by the driver is reduced in dependence on the deceleration proportion of the electric machine.
When in a hybrid vehicle, in which, e.g. the rear axle is electrically driven and which includes a hydraulic brake (=>front/rear split of the brake circuits, i.e. separate brake circuits for front and rear axles which are supplied in tandem construction with hydraulic brake pressure), hydraulic fluid is withdrawn from the brake circuit, associated to the rear axle, to reduce brake power (pressure reduction), the floating piston of the master cylinder compensates this again by overbraking the rear axle as a result of the additional electric braking torque on the rear axle.
WO 2010/083925 A1 discloses an electro-hydraulic brake system for use in vehicles, which can be decelerated by a generator mode of an electric drive motor. The braking system has i.a. a brake booster and an electronic control unit which is provided for distributing the braking action between a generative component or recuperation braking component and a friction brake component. To optimize the pressure medium intake, in particular during recuperation braking operations, it is proposed according to the invention to design the brake booster such that it can be electrically actuated by the electronic control unit.
DE 2625713 A1 discloses a two-circuit system for motor vehicles with a shiftable master cylinder which includes two pressure spaces for the two brake circuits, of which the pressure space for the front axle brake circuit has a larger cross section than the pressure space for the rear axle brake circuit and which are connected with each other by a line extending externally of the master brake cylinder. A shifting valve operating in dependence on the vehicle load is arranged in this line to establish and to interrupt the connection between the two pressure spaces. An intermediate piston, which is arranged between the two pressure spaces in the master cylinder coaxial to the two pressure pistons, is freely movable within a guide sleeve of smaller diameter and is provided with central extensions on both sides thereof for the mechanical cooperation with the two pressure pistons. The two-circuit system is characterized in that the shifting valve is shiftable as a function of the load, of the pressure prevailing in the brake cylinder, and of the deceleration attainable with this pressure.
A generic brake system for a motor vehicle is known from DE 10 2011 008 928 A1.